Recent behavioral and neural evidence suggests that some bitter stimuli may be capable of activating ion channels in the anterior portion of the oral cavity in rodents, while other nonionic bitter stimuli may be limited to activation of the posterior region of the mouth. This series of experiments is designed to examine how the sensation of bitterness is encoded by the central gustatory system, specifically with regard to how this nformation might change depending on the receptive fields stimulated and the chemical structure of bitter stimuli used. This will be accomplished by recording action potentials from single neurons in the gustatory regions of nucleus of the solitary tract and parabrachial nucleus, while stimulating the more posterior receptive fields (i.e. the foliate and circumvallate papillae) with a variety of taste stimuli. Although the glossopharyngeal nerve, which innervates these papillae, is highly sensitive to bitter stimuli, their contribution to taste perception at the level of the CMS has not been established. This may be due in part to the fact that additional measures, including sutures and pipettes, are necessary to effectively stimulate these receptive fields. A psychophysical experiment will also be performed so that parallels can be drawn between responses at the level of the CNS and bitter taste perception in awake animals. This will be accomplished by severing sets of peripheral gustatory nerves prior to behavioral testing with bitter stimuli so that the influence of taste receptor cells in the fields innervated by these nerves can be determined. Although we typically think of bitter-tasting foods as being toxic, a number of vitamin-rich foods, such as broccoli and kale, have also been described as tasting bitter by human subjects. If we can better understand how bitter taste is encoded by the gustatory system, perhaps this information could be used to improve the taste of certain medications and/or healthy foods.